For a Solo(k), is rental income equal to self-employment Income?

[Keith N.]

I apologize if this has already been answered.  I tried searching for the answer to my question, but was unable to find it.

I just finished reading the BP book on tax strategies and am interested in setting up a solo 401(k).  One of the requirements is that there must be self-employment income.  I don't sell, flip, wholesale, or have any other income that would be schedule C.  I have 17 units that generate rental income.  I know that rental income isn't subject to self-employment taxes, but is it considered self-employment income for purposes of funding a solo(k)?  I appreciate your help.